Allergies are the body's overreaction to certain substances. When you come in contact with something you're allergic to, your immune system flags it as harmful and sends out antibodies to attack it. The antibodies cause the release of chemicals including histamine, which is responsible for most of the allergic symptoms you're familiar with. The most common allergies are to foods, dust, pollen and mold. Some people are sensitive to insect stings or medications, too.

Lavender is an herb that's often utilized for its calming properties. Though the small lavender bush is native to Mediterranean regions, it also grows in Europe, Australia and the United States. Lavender oil can cause allergic reactions in some people when they touch it or inhale it; the symptoms include nausea, vomiting, chills and headaches. Other common signs of allergies include rashes, hives and cold-like symptoms. A doctor can determine whether your symptoms are allergy-related.